Process for forming peelable seals

ABSTRACT

A process for forming peelable seals between a layer of spunbonded olefin material and an unsupported film of polyethylene or to a supported film of a laminated or coated backing, such as polyethylene coated Mylar, to form a peel-seal packet, container or pouch. The spunbonded olefin material is first pretreated with a heated die in the areas that are to form the peel-seal with heat and pressure suitable to render uniform surface characteristics to the spunbonded olefin. The heat, pressure and dwell time of the pretreatment are sufficient to eliminate the high spots and internal weaknesses of the spun-bonded olefin material following which a web of synthetic polymeric material having a heat sealable surface may be peelably sealed by a conventional heat sealing method.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my co-pending applicationSer. No. 499,621, filed Aug. 22, 1974, now U.S. Pat. No. 3,926,311, Dec.16, 1975.

Spunbonded olefin sheets such as sold under the registered trademarkTYVEK by DuPont, have gained use for various types of containers.Spunbonded olefin sheets are tough, durable sheets of high-densitypolyethylene fibers. The sheets are formed by first spinning continuousstrands of very fine interconnected fibers and then bonding themtogether with heat and pressure. The spunbonded olefin has high opacityand it is frequently desirable to have one side of the containertransparent. Thus, it is desirable to produce containers with atransparent sheet such as polyethylene on one side and spunbonded olefinon the other. However, satisfactory peel-seals between the polyethyleneand spunbonded olefin have not previously been obtained, especially withthe required avoidance of tearing demanded for containers of sterilizedmedical goods without coating the spunbonded olefin.

When it was desired to make containers using the spunbonded olefinmaterial on one side and a transparent material such as polyethylene onthe other side, experience has shown that the sealing of polyethylenedirectly to the spunbonded polyolefin material using conventionalsealing processes has caused difficulties. Specifically, upon openingthe container by peeling the polyethylene sheet from the spunbondedolefin, the spunbonded olefin material is frequently fracturedinternally and separated, thus providing an unsatisfactory pouch,particularly for medical uses.

Prior methods that have been used to produce peel-seal containers usingspunbonded olefin have involved coating spunbonded olefin material toprovide a suitable sealing surface for the polyethylene. Coating of thespunbonded olefin material has been a problem due to the uneven surfacecharacteristics and gauge variations of the spunbonded olefin material.The coating of the spunbonded olefin, however, does reduce tearing ofthe spunbonded olefin when peeled from polyethylene, but increases thecost and contamination problems.

Containers have been produced sealing polyethylene to uncoatedspunbonded olefin, but fabrication is very difficult, there being a verynarrow range of temperature, time and pressure tolerances. Some medicaland other uses permit high levels (above about five percent) ofspunbonded olefin tearing upon opening as results from commercialproduction according to prior methods of sealing polyethylene touncoated spunbonded olefin. It is extremely difficult if not impossibleto obtain an acceptably low level (below about five percent) ofspunbonded olefin tearing upon opening such containers as demanded bymany medical uses or other stringent uses where tearing or loose fibersis undesirable.

The process of this invention provides a peel-seal container or pouchwhich is highly reliable in providing extremely low incidence of tearingas demanded for medical uses and which can be produced at less cost thatprior art methods.

The process of this invention involves a sheet of spunbonded olefin anda sheet of synthetic polymeric thermoplastic heat sealable materialbeing fastened to each other by a peel-seal. Satisfactory polymericthermoplastic materials include unsupported polyethylene or may be alaminate such as polyethylene laminated to polyester or a coatedmaterial having a heat seable surface coating, such as polyethyleneapplied to nylon.

The process of this invention involves pretreatment of the spunbondedolefin material by applying a heated die, in the shape of at least aportion of the peel-seal desired, for a definite period of time at apressure and temperature satisfactory to permit the direct applicationof a heat-sealable polymeric film to the spunbonded olefin material byconventional heat sealing techniques. The pretreatment modifies thesurface of the spunbonded olefin by eliminating high spots and renderingthe sealing area susceptible to having a synthetic polymeric materialpeelably joined thereto by conventional heat-pressure sealing methods.Usually it is not desirable to pretreat the whole area of spunbondedolefin since the pretreatment prevents the pouch from being breathableand thus easily sterilized. The spunbonded olefin sheet may comprise theentire side of a container or may comprise a strip or any other shapewhich is attached over an opening in the container material.

A container or pouch may have a peel-seal area that extends to the edgeof the pouch or to the edge of the peel-seal area or it may stop at adistance inward from the edge of the pouch or the edge of the spunbondedolefin sheet leaving the two sheets of material unsealed at the edges.In the latter case, the spunbonded olefin sheet is not sealed to thepolymeric film sheet at the longitudinal edges when multiple pouches aremade from webs of sheet material. In these instances, it is possible topretreat the preseal area according to this invention at one station,providing an area which readily seals a heat sealable polymeric film tothe spunbonded olefin sheet by conventional heat sealing techniques. Thesame result may be obtained by the sealing die having a recess from thesurface of about 0.002 to about 0.005 inch at the outside edges so thata weak seal is obtained at the edge or the recess may be greater and noseal would result at the edge. Of course, the same result may beobtained by a sealing die which is smaller than the outside dimensionsof the spunbonded olefin sheet.

In the instance where it is desired for the peel-seal to extend to theedge of the pouch to avoid contamination and the like, the instances ofthe spunbonded olefin tearing upon opening are greatly increased. Inthese instances, it is preferred that a second pretreatment is appliedto the longitudinal edge areas with slightly higher temperatures andhigher pressures.

Generally, in the manufacture of pouches according to one embodiment ofthis invention, the pouches are made in multiples, that is, two or morepouches across the web of plastic. In these cases, the transparentpolymeric sheet is usually sealed to the spunbonded olefin sheet priorto slitting and cutting the sheets into individual pouches. Thus, it isespecially desirable to provide the second pretreatment to the areaswhich will be slit or cut after sealing when greatest resistance totearing of the spunbonded olefin is desired.

It is also within this invention to provide only the second treatment tothe slitting and cutting areas in cases where the prevention of tearingof the spunbonded olefin sheet is not of utmost importance.

The apparatus for use in making containers according to one embodimentof the process of this invention involves a pretreatment means forpretreatment of spunbonded olefin material in the area where thepeel-seal is to be formed, which may include a first pretreatmentstation for treatment in the entire area of the peel-seal and a secondpretreatment station for treatment at the edge and slitting and cuttingareas and a sealing means where the heat-sealable polymeric film isjoined in the pretreated peel-seal area to the spunbonded olefinmaterial by conventional heat sealing techniques. Following thatoperation the containers may be slit and cut into the desired package,containers or pouches.

The containers made by the process of this invention provide veryacceptable medical type of pouches for containing a large variety ofitems. The containers made according to this invention may also be usedfor packaging any other desired article.

the objects, advantages and features of this invention will be apparentfrom the description together with the drawings showing preferredembodiments, wherein:

FIG. 1 is a perspective of a partially opened container made accordingto the process of this invention;

FIG. 2 is a schematic top view of material as it proceeds through theapparatus of FIG. 3 to produce containers according to the process ofthis invention; and

FIG. 3 is a side view of an apparatus to form containers according tothe process of this invention.

Referring to the drawings in FIG. 1 it will be seen that container 10results from the operation of the method of this invention utilizing theapparatus shown in FIG. 3. Container 10 comprises a sheet of spunbondedolefin material 12, such as TYVEK, a sheet of synthetic polymer material14, for example polyethylene, a peel-seal area 16, and a peel flap 18which provides the mechanism by which the person opening the containercan grip the two layers and separate them along the area of thepeel-seal.

It will be seen in FIG. 1 at the area indicated by 20 that thecharacteristics of the surface of spunbonded olefin of sheet 12 havebeen modified by pretreatment to sufficiently eliminate high spots andinternal weaknesses so that utilizing conventional heat sealingtechniques, sheet 14 can be sealed to the spunbonded olefin sheet toprovide the peel-seal 16. The longitudinal edges have been pretreated ata higher temperature-time-pressure relationship shown as 15.

Open end 22 illustrates one way in which the container of this inventionmay be produced. It should be understood that the end 22 may be leftopen in order that the materials to be packaged can be inserted into thecontainers and then sealed. It is also within the scope of thisinvention to insert the material to be packaged prior to the time of theformation of the peel-seal so that the end 22 can be closed at the sametime and in the same manner as is the remainder of the peel-seal. It iswithin the scope of the process of this invention to provide containersof any desired shape or any other article of sheet spunbonded olefinmaterial in a peel-seal relationship with synthetic polymericthermoplastic material such as polyethylene. For example, the entireside of a container may be made of the spunbonded olefin material asshown in FIG. 1 or only a portion of one side may comprise an area ofspunbonded olefin sheet in peel-seal relation, such as a strip acrossthe side, one end area, or a hole through the side material of anyshape. Such areas having the peel-seal spunbonded olefin sheet coveringare usually used for gaining access to the product, but it is not meantto restrict this invention only to such areas.

Referring to FIG. 3, it will be seen that roll of material 14 isprovided mounted on suitable support, along with another roll 26 ofspunbonded olefin material 12. Rolls 24 and 26 are mounted with suitableunwind mechanisms at the end of machine frame 28. Pretreatment station Ishows pretreatment means 30 comprising base 36 having attached to itframe 32 with drive mechanism 33 and platen 34 holding die 35. The shapeof the portion of die 35 which contacts the web of material 12 is theshape that is desired for the area of pretreatment. Pretreatment stationII, FIG. 3, shows pretreatment means 60 comprising base 66 havingattached to it frame 62 with drive mechanism 63 and platen 64 holdingdie 65.

In FIG. 2, the stations denoted by Roman numerals with respect to theweb of plastic correspond to the stations denoted in FIG. 3.Pretreatment station I imparts the pretreatment at the slitting areasand extreme edges of the finished pouches. As explained above, thetemperature-time-pressure relation is such to give increasedpretreatment in the pretreatment area shown in station I than in theoverall pretreatment area. A suitable die shape to obtain the desiredpretreatment area is readily apparent to one skilled in the art.

As shown in FIG. 2, pretreatment station II imparts the desiredpretreatment to spunbonded olefin over the entire peel-seal area. Thetemperature-time-pressure relation at pretreatment station II is lessthan that used at pretreatment station I.

While FIGS. 2 and 3 show two pretreatment stations, it should beunderstood that this invention encompasses the use of eitherpretreatment station I or pretreatment station II alone, and thecombination of pretreatment stations I and II. Also, it should beunderstood that it is within this invention to reverse the sequence ofpretreatment stations I and II.

Further, while the treatment and sealing dies are shown in FIG. 3 to bereciprocating, it should be understood that this invention includes likedies being mounted on cylinders.

The second layer of material 14 that is to be bonded to the first layer12 is guided into position from roll 24 by a pair of guide rolls 38 inorder that it can be positioned in juxtaposition under sealing means 40at sealing station III. Sealing station III shows sealing means 40comprising base 46 having attached to it frame 42 with drive mechanism43 and platen 44 holding sealing die 45. Again, while sealing die, asshown in FIG. 3, is reciprocating, it can also be rotary. Sealingstation III provides suitable heat and pressure to seal the desiredareas of the sheets together under conventional conditions of heatsealing polymeric materials such as polyolefins. The sealing die atsealing station III may be smaller than the area of the spunbondedolefin so as to provide a non-sealed area around the edge of thespunbonded olefin sheet. When it is desired to seal to the edge of thespunbonded olefin sheet and only the first above pretreatment has beeneffected, the die may have a step-recess of about 0.002 to about 0.005inch at the edge so that a weak seal is formed at the edges of thespunbonded olefin sheet.

Slitting station IV shows slitting means 50 comprising rollers 51 and 52which longitudinally slits the moving web in the desired locations asshown in FIG. 2 at station IV.

Draw rollers 48 and 49 draw the plastic webs through the machine withindexing controlled by electric eye or mechanical measuring. Afterpassing through draw rollers 48 and 49 the plastic web passes throughshearing station V having shearing means 55 comprising knife 56 andanvil 57. At shearing station V containers are cut transversly and maybe collected by any suitable means such as conveyor 58. The finishedpouches are shown in FIG. 2 at station VI corresponding to the conveyormeans.

The process of this invention may comprise drawing a web of spunbondedolefin material to a pretreatment station. At the pretreatment stationthe spunbonded olefin sheet is treated in one or both of twopretreatment operations by subjecting the peel-seal area of thespunbonded olefin to heat and pressure for a time sufficient to renderthe peel-seal area susceptible to conventional heat sealing to a secondpolymeric thermoplastic sheet material. It will be obvious to oneskilled in the art that the apparatus and methods shown in FIGS. 2 and 3are merely exemplary of one method of making a particular pouch and thatother methods and apparatus well known in the art may be utilized forfabrication of other shapes and configurations of containers. Thisinvention relates to the process for forming the peelable sealsregardless of configuration.

One pretreatment of this invention is with suitable pressure and heat tothe whole area to be sealed. It has been found for pretreatment ofspunbonded olefin sheets of about 0.008 inch thickness and density ofabout 2.2 ounces per 1000 square inches, that temperatures of about 265°to about 290° F. are suitable for this pretreatment with a dwell time ofabout three-quarter to about two seconds at a pressure of about 40 toabout 80 psig. The temperature-time-pressure treatment parameters may bechanged somewhat with differing thicknesses or densities of thespunbonded olefin sheet. These adjustments may be readily ascertained toachieve desired pretreatment. When the higher temperature is used thetime and/or pressure componenets should be reduced and conversely whenthe temperatures are in the lower portion of the range, higher timesand/or pressures are suitable. It has been found especially suitable touse for the entire seal area pretreatment a temperature of about 280°F., dwell time about 1.8 seconds and pressure about 50 psig. Thepretreatment as disclosed in this paragraph may be achieved inpretreatment station II shown in FIGS. 2 and 3.

Another pretreatment of this invention is with suitable pressure andheat to the areas of the spunbonded olefin which form the edges of thearea of the peel-seal connection. It has been found for pretreatment ofspunbonded olefin sheet of about 0.008 inch thickness and density ofabout 2.2 ounces per 1000 square inches that temperatures of about 275°to about 300° F. are suitable for this pretreatment with a dwell time ofabout one-half to about 2 seconds at a pressure of about 60 to about 100psig. The temperature-time-pressure treatment parameters may be changedsomewhat with differing thicknesses or densities of the spunbondedolefin sheet. These adjustments may be readily ascertained to achievedesired pretreatment. When the higher temperature is used the timeand/or pressure components should be reduced and conversely when thetemperatures are in the lower portion of the range, higher times and/orpressures are suitable. It has been found especially suitable to use forthe edge pretreatment a temperature of about 290° F., dwell time about1.5 seconds and pressure about 70 psig. The pretreatment as disclosed inthis paragraph may be achieved in pretreatment station I shown in FIGS.2 and 3.

The two pretreatments are preferred to produce peel-seal containers withthe minimum incidence of tearing the spunbonded olefin upon opening.Containers produced according to this invention having the abovepretreatments have shown an incidence of tearing of the spunbondedolefin visible to the naked eye of less than three percent. Previous tothis invention, I have found uncoated spunbonded olefin sheets sealed topolyethylene produced tearing upon opening peel-seals with a frequencymuch higher than acceptable for medical containers.

It should be understood that, though the use of unsupported polyethylenefilm is described in the above specific examples as the material 14,that anything which can be heat sealed to spunbonded olefin, such as acoated polypropylene, can also be used as within the teachings of thisinvention.

While in the foregoing specifications this invention has been describedin relation to certain preferred embodiments thereof, and many detailshave been set forth for purpose of illustration, it will be apparent tothose skilled in the art that the invention is susceptible to additionalembodiments and that certain of the details described herein can bevaried considerably without departing from the basic principles of theinvention.

I claim:
 1. A method for forming peelable seals between uncoatedspunbonded olefin sheet material and a synthetic polymeric thermoplasticsheet material comprising maintaining a substantial portion of saidspunbonded olefin sheet untreated and breathable, modifying the surfaceof the spunbonded olefin sheet in the area of the desired peelable sealby pretreatment with heat and pressure to sbustantially eliminate highspots and internal weaknesses to render the sealing area susceptible tohaving said synthetic polymeric thermoplastic material peelably joinedthereto in said pretreated area by conventional heat-pressure sealing,and peelably sealing said pretreated spunbonded olefin sheet to saidsynthetic polymeric thermoplastic sheet material by conventionalheat-pressure sealing only in said pretreated area.
 2. The method ofclaim 1 wherein said pretreatment is performed at temperatures of about265° to about 290° F. with a dwell time of about three-quarter to about2 seconds at a pressure of about 40 to about 60 psig to the entirepeel-seal area.
 3. The method of claim 1 wherein said pretreatment isperformed at temperatures of about 275° to about 300° F. with a dwelltime of about one-half to about 2 seconds at a pressure of about 60 toabout 100 psig to the peel-seal area at the edges of the peel-seal area.4. The method of claim 1 wherein a first pretreatment step is performedat temperatures of about 265° to about 290° F. with a dwell time ofabout three-quarter to about 2 seconds at a pressure of about 40 toabout 60 psig to the entire peel-seal area and a second pretreatmentstep is performed at temperatures of about 275° to about 300° F. with adwell time of about one-half to about 2 seconds at a pressure of about60 to about 100 psig to the peel-seal area at the edges of the peel-sealarea.
 5. The method of claim 1 wherein said synthetic polymericthermoplastic material is selected from the group consisting ofpolyethylene, a laminate having polyethylene as a surface, and a coatedmaterial having a heat sealable surface coating.
 6. The method of claim5 wherein said synthetic polymeric thermoplastic material is sheetpolyethylene.
 7. The method of claim 1 wherein said seal stops at adistance inward from the edge of said spunbonded olefin sheet material.8. The method of claim 1 wherein said seal is obtained by the sealingdie having a recess from the surface at the outside edges so that a weakseal is obtained at the edge.
 9. The method of making a peel-sealcontainer which comprises steps of:drawing a first web of an uncoatedspunbonded olefin material into a pretreatment area; subjecting thepeel-seal area of said uncoated spunbonded olefin to heat and pressurefor a time sufficient to modify the surface in the area of saidpeel-seal to substantially eliminte the high spots and internalweaknesses to render said desired sealing area susceptible to having asecond sheet of heat sealable synthetic polymer material peelably joinedthereto by conventional heat-pressure sealing while maintaining asubstantial portion of said spunbonded olefin web untreated andbreathable; drawing a second web of a heat sealable synthetic polymericmaterial into an overlying relationship to said first web; andsubjecting both said layers to heat and pressure for a time sufficientto cause said layers to be peelably joined together only in thepeel-seal area.